The invention relates to a method for controlling a hybrid vehicle.
Hybrid electric vehicles contain a primary energy source (engine) and a secondary energy storage (Rechargable Electric Energy storage). There is at least one electric motor drives (electric motor, power-electronic frequency converter and control unit) that can provide power to the battery for charging, that can brake regeneratively and/or can assist the engine in providing tractive force to the vehicle.
For hybrid electric vehicles equipped with batteries or ultra-capacitors or the like, often auxiliary systems are powered by the traction battery instead of from a mechanical belt or similar from the engine. The reason for this can be to enable electric-only driving (with engine shut-off), to shut off engine to reduce engine idling and/or to obtain an increased efficiency.
Examples of auxiliaries that can be driven by electric motors are brake air compressors, steering servo oil pumps, 12V or 24V alternators (that can be replaced by static power electronic DC/DC voltage converters, etc.
The battery is equipped with a breaker in order to isolate the battery voltage at shut-off, to de-energize electric circuits at shut-off and to interrupt current at failures.
The electric Motor Drive System (MDS), consists of or comprises an electric motor/machine, a power electronic AC/DC converter and associated Electronic Control Unit (ECU). If the electric motor is permanently magnetized (PM motor), its no-load voltage will be dependant on the motor speed. Usually, the no-load voltage is proportional to the speed.
The problem is that if the MDS control fails, it is not possible to control the electric energy flows and the battery power. Since the electric auxiliary loads continues to consume power, they will deplete the battery state-of-charge, and the battery will have to be disconnected to prevent severe battery damage. When the power supply for the auxiliaries disappears, this can deteriorate the vehicle functionality in an unfavourable way. For example, if the brake air compressor is driven from the battery voltage, battery breaker opening will cause stop-on-road for the vehicle, even if the rest of the powertrain (engine, transmission, etc) is fully operational.
It is desirable to provide a method for prohibiting an accidental stop-on-road for a hybrid vehicle in case of failure in the electric motor drive system.
In a first example embodiment according to an aspect of the invention it is provided a method for controlling a hybrid vehicle in an emergency situation, said hybrid vehicle comprising an internal combustion engine, a rechargeable electric energy storage system, an electrical motor drive system, said method comprising the actions of: detecting a failure of a control unit for controlling the electrical motor drive system, disconnecting the rechargeable electric energy storage system from the hybrid vehicle, limiting the maximum speed of the internal combustion engine from a first RPM value to a second RPM value. Said second value is lower than said first value.
An advantage with said example embodiment of the present invention is that no extra equipment has to be added in order to solve the availability for the auxiliary components.
Another advantage of an aspect of the present invention is that it is lighter, smaller and less expensive compared to existing solutions.
In another example embodiment according to the present invention said method further comprising the step of limiting the minimum speed of the internal combustion engine from a first RPM value to a second RPM value where said second value is higher than said first value.
An advantage of this example embodiment is that it ensures sufficient voltage supply to the auxiliary components with no extra equipment used.
In another example embodiment of the present invention said method further comprising the step of changing the gear choices of an automated transmission from a first set of gear choices, which is used when the control unit controlling the electrical motor drive system is functioning, to a second set of gear choices for the altered upper and/or lower engine speed of the hybrid vehicle when the control unit controlling the electrical motor drive system is not functioning.
An advantage of this example embodiment is that the drivability is secured irrespective of the functionality of the control unit for controlling the electrical motor drive system.
In another example embodiment of the present invention said method further comprising the action of allowing the engine to run under said minimum speed in case of energy reserves provided by at least one auxiliary loads.
An advantage of this example embodiment is that the fuel consumption and exhaust emissions may be kept at a minimum level.
In another aspect of the present invention it is provided a An apparatus for controlling a hybrid vehicle in an emergency situation. Said hybrid vehicle comprising an internal combustion engine, a rechargeable electric energy storage system, an electrical motor drive system. Said apparatus comprising: means for detecting a failure of a control unit for controlling the electrical motor drive system, means for disconnecting the rechargeable electric energy storage system from the hybrid vehicle, means for limiting the maximum speed of the internal combustion engine from a first RPM value to a second RPM value.
In still another aspect of the present invention it is provided a computer program storable on a computer readable medium, comprising a program code for use in an on-board-diagnosis method for controlling a hybrid vehicle in an emergency situation, said method comprising the actions of detecting a failure of a control unit controlling the electrical motor drive system, disconnecting the rechargeable electric energy storage system from the hybrid vehicle, limiting the maximum speed of the internal combustion engine from a first RPM value to a second RPM value.
In the drawings, equal or similar elements are referred to by equal reference numerals. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. Moreover, the drawings are intended to depict only typical embodiments of the invention and therefore should not be considered as limiting the scope of the invention.